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Stifflers

FIT Subframe System Chassis Stiffening Kit

$569.95 $559.99 Save $9.96

SKU: FIT-M02

In Stock
In Stock
Ships by Sep 13
Free Shipping over $200
$100 Minimum Order
30 Days Return
INSTALL DIFFICULTY
DIY PRO SHOP

Moderate — 2–4 hours

Overview

The Stifflers FIT Subframe System is a modular chassis stiffening kit designed for 1979-1993 Mustangs. It integrates subframe connectors, stiffening rails, and a web brace to enhance chassis stiffness and strength. This system is optimized to improve ride quality, handling, and suspension tuning range by reducing chassis twisting.

The FIT System is constructed from mild steel tubing and features a Slide-2-Size mounting system for easier installation of the web brace. The weld locations are free of powder coat to save preparation time. The non-intrusive design does not require floor cutting or interior removal, and it maintains factory ground clearance.
Show original supplier description
The Stifflers FIT Subframe System is a comprehensive chassis reinforcement solution engineered for 1979-1993 Mustangs. This modular system integrates three key components—subframe connectors, stiffening rails, and a web brace—to significantly enhance the chassis's stiffness and overall strength. By reducing chassis flex, the FIT System enables more efficient power transfer to the ground, facilitates straighter launches, and improves handling precision. It also contributes to a reduction in interior rattles and can extend the vehicle's lifespan. The innovative Slide-2-Size mounting system simplifies the installation of the web brace, making the process more manageable. To further streamline installation, the weld locations are intentionally left free of powder coating, saving valuable prep time. Additionally, it increases side impact safety. Installation of the Stifflers FIT Subframe System requires welding and is recommended for experienced installers. Instructions are available for download to guide the process. A specific exception applies to 1987-1993 convertible models, where the stiffening rail component is not required and should be omitted from the installation. The system is otherwise designed to fit 1979-1993 Mustangs.

Product descriptions are provided by our supplier partners and may not always be perfectly accurate. Not sure this fits? or call (760) 282-4645 and we’ll verify before you order.

Fitment

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Specifications

BrandStifflers
Part NumberFIT-M02
CategoryChassis Components

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Returns & Fitment

Built for enthusiasts. Every order is backed by our 30 day return window on eligible items. Unused and uninstalled products may be returned with approved RMA and no restocking fees when received in new condition. Orders placed through the MOTORMIA app with a complete build qualify for our Fitment Guarantee — free return shipping if the part doesn’t fit your exact setup. The guarantee covers fit only; installation must follow manufacturer instructions, and we recommend a qualified shop for parts marked Difficulty 4–5.

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Shipping

Orders are processed in 1–3 business days. In stock parts ship promptly from our partner network. Special-order items either aren’t currently stocked or are built to your spec — expect 4–6 weeks. If a part goes on backorder while your order is in the queue, we’ll reach out and work through discounted alternatives together.

Free shipping over $200 in the continental US. Alaska, Hawaii, U.S. territories (Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, and the Northern Mariana Islands), and international orders carry surcharges — most appear at checkout. Some exceptions (LTL freight, or suppliers who quote freight only after we place the order) won’t. In those cases we’ll reach out with the exact charge before your order moves forward.

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